Search Results (34)

The structural and magnetic properties and band structure results of HoCo_3−xSi_x compounds are reported. First-principles GGA+U+SO calculations, compared with magnetometry experiments, provide deep insight on the magnetic properties of the HoCo₃ compound. They show that HoCo₃ is a robust ferrimagnet, with strongly localized Ho-4f moments in excellent agreement with neutron data and itinerant Co-3d magnetism, where inclusion of the interstitial contribution brings the Co moments into very good agreement with the experimental data. The electronic structure reveals sharp Ho-4f states well below E_F, exchange-split Co-3d bands crossing E_F, and noticeable Ho-5d–Co-3d hybridization that mediates the antiparallel Ho–Co coupling and explains the non-negligible interstitial moment, providing a consistent microscopic picture that supports the experimentally observed increase in magnetization upon Co-Si substitution. Metamagnetic transitions are shown in magnetization isotherms. The observed transitions are broad and can be explained by the distribution of internal magnetic fields which arises from differences in the local environments of cobalt atoms. The magnetic properties were correlated with the theoretical results. Two transitions were revealed below room temperature, one due to a transition to a noncollinear magnetic structure and the other due to a temperature-induced metamagnetic transition. Full article

In the present paper, we discuss the thermodynamic and dynamic phase transition properties of the kinetic Blume–Capel model with spin-1, defined on non-regular lattices, namely decorated simple cubic, decorated triangular, and decorated square (Lieb) lattice geometries. Benefiting from the recent results obtained for the thermodynamic phase transitions of the aforementioned lattice topologies [Azhari, M. and Yu, U., J. Stat. Mech. (2022) 033204], we explore the variation of the dynamic order parameter, dynamic scaling variance, and dynamic magnetic susceptibility as functions of the amplitude, bias, and period of the oscillating field sequence. According to the simulations, a second-order dynamic phase transition takes place at a critical field period for the systems with zero bias. A particular emphasis has also been devoted to metamagnetic anomalies emerging in the dynamic paramagnetic phase. In this regard, the generic two-peak symmetric behavior of the dynamic response functions has been found in the slow critical dynamics (i.e. dynamic paramagnetic) regime. Our results yield that the characteristics of the dynamic phase transitions observed in the kinetic Ising model on regular lattices can be extended to such non-regular lattices with a larger spin value. Full article

This study explores the structural, magnetic, and magnetocaloric properties of ${\mathrm{Ce}}_2$(Fe, Co${)}_{17}$ (x = 0, 0.5, 0.6, and 0.7) compounds synthesized via arc melting under high temperatures exceeding 2300 K. The as-cast ingots are subsequently sealed and subjected to a heat treatment at 1323 K to improve homogeneity and crystallinity. Detailed analyses using X-ray diffraction and magnetometry reveal that cobalt substitution significantly impacts the structural and magnetic behavior, enabling precise tuning of the magnetic transition temperature and magnetic order. The substitution induces an anisotropic increase in cell parameters and shifts the magnetocaloric effect (MCE) from low temperatures (200 K for x = 0) to near room temperature (285 K for x = 0.7), enhancing the operating temperature range. The magnetocaloric effect is studied across different magnetic transitions: a metamagnetic and ferro-antiferromagnetic transition followed by a paramagnetic state in one sample, and a direct ferro-paramagnetic transition in another. The compounds exhibit a second-order magnetic phase transition, ensuring a reversible MCE, with a relative cooling power (RCP) that is approximately 85% of that of pure Gd. Moreover, the use of cerium, the most cost-effective rare-earth element (5 $/kg), combined with its low atomic concentration (10%) in these intermetallics, enhances the sustainability and affordability of these materials. These findings underline the potential of iron-rich Ce-based compounds for next-generation refrigeration and energy-harvesting applications. Full article

In this study, we aimed to induce controlled structural disorder through a double substitution approach in the La_0.5Ca_0.5MnO₃ compound by investigating La_0.5−xRe_xCa_0.5−yAe_yMnO₃ compounds with x = 0.05 and 0.1 and Re = Eu, Nd, Gd, Pr, and Ae = Ba and Sr. The y values are adjusted to maintain a constant average ionic radius (<r_A> = 1.198 Å) and an unchanged Mn^3+/Mn⁴⁺ ratio. These samples were synthesized using the sol–gel method. XRD analysis confirms structural stability despite the induced disorder, showing subtle lattice distortions. Magnetic measurements reveal that introducing low disorder annihilates the charge ordered (CO) state, enhances double-exchange interactions, and influences the ferromagnetic (FM) volume fractions. Moderate disorder strengthens AFM–CO state, triggering a first–order metamagnetic transition and reducing the Curie temperature value. Magnetic field-dependent magnetization data show disorder dependent magnetic behavior and suggest the presence of the Griffiths phase for all samples, confirming the role of structural disorder in tuning magnetic phase coexistence. Pr-based samples display a considerable magnetocaloric effect near their Curie temperature. Full article

In this paper, the impact of annealing at different temperatures (973 K, 1073 K, and 1123 K for 1 h) on the magnetic and microstructural properties of MnFePSi-based glass-coated microwires is studied. Annealing significantly influences the magnetic and microstructural properties of Mn–Fe–P–Si glass-coated microwires. XRD analysis reveals that increasing the annealing temperature leads to a notable increase in the Fe₂P phase content, reaching a maximum at 1123 K, while simultaneously reducing the presence of secondary phases observed in the as-prepared sample. The reduction in secondary phases in Mn–Fe–P–Si-based microwires, grain size, and internal stress relaxation have a profound impact on their magnetic behavior. High coercivity values are observed in both the as-prepared and annealed samples. However, annealing at higher temperatures (1073 K and 1123 K) results in a significant reduction in coercivity, decreasing from 1200 Oe for the sample annealed at 973 K to 300 Oe and 150 Oe, respectively. In addition, the sample annealed at 1123 K for 1 h shows a notable paramagnetic behavior for loops measured from 200 K to 300 K. Meanwhile, the other samples show ferromagnetic behavior for all measured temperatures from 5 to 300 K. This study highlights the significant potential for tailoring and modifying various magnetic properties of Mn–Fe–P–Si glass-coated microwires, including metamagnetic phase transitions, magnetic behavior, and the control of magnetic response (hardness/softness). Such tailored properties make Mn–Fe–P–Si glass-coated microwires promising candidates for a wide range of applications. Full article

This paper reports the results of a systematic investigation into the magnetic properties of Bi_1−yCa_yFe_1−xMn_xO₃ (0.1 ≤ y ≤ 0.175, 0.35 ≤ x ≤ 0.45) solid solutions. The substitution of Bi³⁺ with Ca²⁺ and the concurrent introduction of Mn³⁺/Mn⁴⁺ ions result in the stabilization of various structural phases, with each exhibiting distinct magnetic characteristics. The investigation indicates that the samples containing the polar rhombohedral phase display metamagnetic transitions at low temperatures, characterized by pronounced jumps in magnetization. Single-phase samples with a nonpolar orthorhombic structure exhibit weak ferromagnetic behavior without metamagnetic features. The observed metamagnetic behavior, accompanied by anomalies in temperature-dependent magnetization and significant remnant magnetization at low temperatures, particularly in samples near the polar-anti(non)polar phase boundary, highlighted the presence of both antiferromagnetic and glassy magnetic components. Full article

Direct measurements of the magnetocaloric effect were performed in a Heusler Ni_44.4Mn_36.2Sn_14.9Cu_4.5 alloy at cryogenic temperatures in magnetic fields up to 10 T. The maximum value of the inverse magnetocaloric effect in a 10 T field was ∆T_ad = –2.7 K in the vicinity of the first-order magnetostructural phase transition at T₀ = 117 K. Ab initio and Monte Carlo calculations were performed to discuss the effect of Cu doping into a Ni-Mn-Sn compound on the ground-state structural and magnetic properties. It is shown that with increasing Cu content the martensitic transition temperature decreases and the Curie temperature of austenite slightly increases. In general, the calculated transition temperatures and magnetization values correlated well with the experimental ones. Full article

In this study, magnetostriction measurements were performed on the ferromagnetic Heusler alloy, Ni₂MnGa_0.88Cu_0.12, which is characterized by the occurrence of the martensitic phase and ferromagnetic transitions at the same temperature. In the austenite and martensite phases, the alloy crystallizes in the L2₁ and D0₂₂-like crystal structure, respectively. As the crystal structure changes at the martensitic transition temperature (T_M), a large magnetostriction due to the martensitic and ferromagnetic transitions induced by magnetic fields is expected to occur. First, magnetization (M-H) measurements are performed, and metamagnetic transitions are observed in the magnetic field of μ₀H = 4 T at 344 K. This result shows that the phase transition was induced by the magnetic field under a constant temperature. Forced magnetostriction measurements (ΔL/L) are then performed under a constant temperature and atmospheric pressure (P = 0.1 MPa). Magnetostriction up to 1300 ppm is observed around T_M. The magnetization results and magnetostriction measurements showed the occurrence of the magnetic-field-induced strain from the paramagnetic austenite phase to the ferromagnetic martensite phase. As a reference sample, we measure the magnetostriction of the Ni₂MnGa-type (Ni₅₀Mn₃₀Ga₂₀) alloy, which causes the martensite phase transition at T_M = 315 K. The measurement of magnetostriction at room temperature (298 K) showed a magnetostriction of 3300 ppm. The magnetostriction of Ni₂MnGa_0.88Cu_0.12 is observed to be one-third that of Ni₅₀Mn₃₀Ga₂₀ but larger than that of Terfenol-D (800 ppm), which is renowned as the giant magnetostriction alloy. Full article

The YbCoC₂ compound, which crystallizes in a base-centered orthorhombic unit cell in the $Amm2$ space group CeNiC₂ structure, is unique among Yb-based compounds due to the highest magnetic ordering temperature of $T_N=27$ K. Magnetization measurements have made it possible to plot the H-T magnetic phase diagram and determine the magnetocaloric effect of this recently discovered high-temperature heavy-fermion compound, YbCoC₂. YbCoC₂ undergoes spin transformation to the spin-polarized state through a metamagnetic transition in an external magnetic field. The transition is found to be of the first order. The dependencies of magnetic entropy change $\Delta S_m\left(T\right)$—have segments with positive and negative magnetocaloric effects for $\Delta H\le 6$ T. For $\Delta H=9$ T, the magnetocaloric effect becomes positive, with a maximum $\Delta S_m\left(T\right)$ value of 4.1 J (kg K)⁻¹ at $T_N$ and a refrigerant capacity value of 56.6 J kg⁻¹. Full article

The effect of a high magnetic field up to 12 T and a high hydrostatic pressure up to 12 kbar on the stability of the metamagnetic isostructural phase transition and the multicaloric effect of Fe₄₉Rh₅₁ alloy has been studied. The phase transition temperature shifts under the magnetic field and the hydrostatic pressure on with the rates of dT_m/μ₀dH = −9.2 K/T and dT_m/dP = 3.4 K/kbar, respectively. The magnetocaloric and multicaloric (under two external fields) effects were studied via indirect method using Maxwell relations. The maximum of the entropy change is increasing toward the high temperature region from ∆S~2.5 J/(kg K) at 305 K to ∆S~2.7 J/(kg K) at 344 K under simultaneously applied magnetic field of 0.97 T and hydrostatic pressure of 12 kbar. The obtained results were explained using the first-principle calculations of Gibbs energies and the phonon spectra of the ferromagnetic and the antiferromagnetic phases. Taking into account the low concentration of antisite defects in the calculation cells allows us to reproduce the experimental dT_m/dP coefficient. Full article

The inherent existence of multi phases in iron oxide nanostructures highlights the significance of them being investigated deliberately to understand and possibly control the phases. Here, the effects of annealing at 250 °C with a variable duration on the bulk magnetic and structural properties of high aspect ratio biphase iron oxide nanorods with ferrimagnetic Fe₃O₄ and antiferromagnetic α-Fe₂O₃ are explored. Increasing annealing time under a free flow of oxygen enhanced the α-Fe₂O₃ volume fraction and improved the crystallinity of the Fe₃O₄ phase, identified in changes in the magnetization as a function of annealing time. A critical annealing time of approximately 3 h maximized the presence of both phases, as observed via an enhancement in the magnetization and an interfacial pinning effect. This is attributed to disordered spins separating the magnetically distinct phases which tend to align with the application of a magnetic field at high temperatures. The increased antiferromagnetic phase can be distinguished due to the field-induced metamagnetic transitions observed in structures annealed for more than 3 h and was especially prominent in the 9 h annealed sample. Our controlled study in determining the changes in volume fractions with annealing time will enable precise control over phase tunability in iron oxide nanorods, allowing custom-made phase volume fractions in different applications ranging from spintronics to biomedical applications. Full article

We report a possible coexistence of nontrivial topology and antiferromagnetism in the newly discovered compounds EuCdBi${}_2$, with magnetic Eu layer locating above and below Bi square net. The X-ray diffraction on single crystals and powder indicats that this 112-type material crystalizes in space group of $I4/mmm$, the same as SrMnBi${}_2$ and EuMnBi${}_2$. Our combined measurements of magnetization, electrical transport and specific heat consistently reveal antiferromagnetic (AFM) transition of Eu${}^{2+}$ moments at $T_N$ = 20 K. The Eu moments are not saturated under a field of 7 T at 1.8 K. The anisotropic susceptibility suggests the Eu moments lie in the $ab$ plane, and a metamagnetic (MM) transition is observed near 1 T below $T_N$. Large positive magnetoresistance (MR) present for both $H\Vert ab$ and $H\Vert c$, which are considered to contain part contributions from Dirac bands. Hall measurements show the electron-hole compensation effect is prominent above 100 K, with a crossover of Hall resistance from negative to positive values at ∼150 K. The fitted mobility of electrons is as high as 3250 cm${}^2$ V${}^{-1}$ S${}^{-1}$ at 1.8 K. Interestingly, the rapid increase of carrier density and suppression of mobility appear at around $T_N$, indicating non-negligible interaction between Eu moments and electron/hole bands. EuCdBi${}_2$ may provide a new platform to investigate the interplay of topological bands and antiferromagnetic order. Full article

Magnetic anisotropy strongly influences the performance of the magnetocaloric effect. We investigated the magnetocaloric properties of the NdAlGe single crystal with I4₁md structure. The temperature-dependent magnetization revealed significant anisotropic properties; stable antiferromagnetic transition at T_N = 6 K for H//a and meta-magnetic spin reorientation at low temperature (T ≤ 5 K) within an intermediate field (H = 2 T) for H//c. During the metamagnetic spin reorientation, the abrupt change of the magnetic entropy leads to a significant magnetocaloric effect with negative magnetic entropy change (∆S_M) by −13.80 J kg⁻¹ K⁻¹ at T_C = 5.5 K for H = 5 T along the H//c axis. In addition, the antiferromagnetic state for H//a shows the inverse magnetocaloric effect(I-MCE) by positive entropy change ∆S_M = 2.64 J kg⁻¹ K⁻¹ at T_N = 6 K for H = 5 T. This giant MCE accompanied by the metamagnetic transition resulted in a significantly large relative cooling power (158 J/kg at H = 5 T) for H//c. The giant MCE and I-MCE can be applied to the rotational magnetocaloric effect (R-MCE) depending on the crystal orientations. NdAlGe exhibits rotational entropy change ∆S_c−a = −12.85 J kg⁻¹ K at T_peak = 7.5 K, H = 5 T. With comparison to conventional MCE materials, NdAlGe is suggested as promising candidate of R-MCE, which is a novel type of magnetic refrigeration system. Full article

Mixed-valent Ba₂Mn²⁺Mn₂³⁺(SeO₃)₆ crystallizes in a monoclinic P2₁/c structure and has honeycomb layers of Mn³⁺ ions alternating with triangular layers of Mn²⁺ ions. We established the key parameters governing its magnetic structure by magnetization M and specific heat C_p measurements. The title compound exhibits a close succession of a short-range correlation order at T_corr = 10.1 ± 0.1 K and a long-range Néel order at T_N = 5.7 ± 0.1 K, and exhibits a metamagnetic phase transition at T < T_N with hysteresis most pronounced at low temperatures. The causes for these observations were found using the spin exchange parameters evaluated by density functional theory calculations. The title compound represents a unique case in which uniform chains of integer spin Mn³⁺ (S = 2) ions interact with those of half-integer spin Mn²⁺ (S = 5/2) ions. Full article

Giant magnetostriction could be achieved in MnCoSi-based alloys due to the magneto-elastic coupling accompanied by the meta-magnetic transition. In the present work, the effects of hydrostatic pressure on magnetostrictive behavior in MnCo_0.92Ni_0.08Si alloy have been investigated. The saturation magnetostriction (at 30,000 Oe) could be enhanced from 577 ppm to 5034 ppm by the hydrostatic pressure of 3.2 kbar at 100 K. Moreover, under a magnetic field of 20,000 Oe, the reversible magnetostriction was improved from 20 ppm to 2112 ppm when a hydrostatic pressure of 6.4 kbar was applied at 70 K. In all, it has been found that the magnetostrictive effect of the MnCo_0.92Ni_0.08Si compound is strongly sensitive to external hydrostatic pressure. This work proves that the MnCoSi-based alloys as a potential cryogenic magnetostrictive material can be modified through applied hydrostatic pressure. Full article